The influence of guest-host interactions on the excited-state properties of dioxorhenium(V) ions in intracrystalline environments of complex-layered oxides

Abstract

C0),2, 12560-48-4; H~R u~( C O )~~. 34438-91-0; (69) Verdonck, J. J.; Jacobs, P. A.; Gent, M.; Poncelet, G.Abstract: The excited-state properties of trans-dioxorhenium(V) ions immobilized in the intracrystalline environments of three complex-layered oxides (CLOs) have been examined. The layered silicate CLOs hectorite and fluorohectorite adsorb tr~ns-ReO~(py)~+ to their negatively charged interlayers by intercalative ion exchange to produce topotactic solids with gallery heights of 6.7 and 9.2 A, respectively. A dioxorhenium CLO of complementary charge, prepared by the addition of NaOH to an aqueous solution containing MgCl2:A1CI3 (1 :2 w/w) and trans-Re02(CN),)-, incorporates the oxoanion between the positive layers of a hydrotalcite-like Mg/Al double hydroxide. Electronic absorption and vibrational spectra of these three CLO intercalates are characteristic of the dioxorhenium ions and are indicative of structurally unperturbed oxo complexes in the CLO intracrystalhe environment. Despite structurally similar intercalated trans-ReOz+ cores, steady-state and time-resolved luminescence experiments reveal that the three CLO intercalates are quite distinct: solid Re02(py)4-hectorite is highly emissive ( & m , , , = 630 nm at 25 " C ) and luminescence spectra display progressions in 900-cm-I ( v , , # ( R e O ) ) and 200-cm-' (u,ls(Re-py)) modes similar to that of the native ion; Re02(py)4-fluorohectorite exhibits broad and featureless emission ( X , , ,at 25 "C) whose intensity is attenuated by a factor of 50 relative to the hectorite compound and, ReO2(CN),-hydrota1cite does not luminesce. The luminescence decay curve of ReOz(py)4-hectorite displays multiexponential form with a major lifetime component of 13.0 ps and a minor lifetime component of 3.9 ps. In contrast, the emission decay of the fluorohectorite intercalate is uniexponential and fast (7 = 0.63 ps). The disparate excited-state properties of the three intercalates are attributed to specific guest-host interactions which mediate the reaction between the trans-ReOz+ core and water in the CLO interlayers.Photochemical processes can significantly be modified with the intercalation of reactants within intracrystalline environments of zeolites,'-4 layered phosphate^,^ and complex-layered oxides ( C L O S ) .~~O Layered silicate clays (LSCs) and layered double 0002-7863/88/1510-3885$01.50/0 0 1988 American Chemical Society Newsham et al. (1) (a) Turro, N. J. Pure Appl. Chem. 1986,58, 1219-1228. (b) Turro, N. J.; Lei, X.-G.; Cheng, C.-C.; Corbin, D. R.; Abrams, L.

The Speciation of Uranium in a Smectite Clay: Evidence for Catalysed Uranyl Reduction

“…The third oxygen contact at 3.45 Ä, observed for the simple uranyl exchanged clays (Figure 3), is believed to result from the lattice oxygens on the inner clay surface. In combination, the lattice spacing of the clay, the dimensions of the hydrated uranyl species and the third uraniumoxygen contact, suggest that the uranyl unit is "keyed" into the hexagonal hole in the clay-silicate layer, in a manner analogous to that seen for ReO^-exchanged hectorite [38]. In this model, the uranium sits at the Center of the hexagonal hole with the axial oxygen atoms oriented along the c-axis perpendicular to the silicon-oxygen planes.…”

Preparation and structure of oxo-rhenium(V) complexes with 7-azaindole

“…Hydroxyl groups are known to quench luminescence for such systems and water molecules are hydrogen-bonded to the Re=O groups in the present dioxo complexes. Solid-state effects have been noted for guest/host complexes involving ~e 0 : type molecules and clays (21). Because of disorder, the rotamer(s) present in the crystal could not be formally identified.…”

Pressure-dependent luminescence spectroscopy of molybdenum(iv) oxo complexes

“…Transition metal complexes with metal-oxo bonds have a rich variety of excited-state properties, extensively probed in the past mainly for metals of the 5d series. [1][2][3][4][5][6][7][8][9][10][11] One of the key aspects of their low-energy electronic transitions is the influence of strong spin-orbit coupling between the ground state and excited states of identical symmetry, leading to distinct vibronic signatures. 8, 10 Under external pressure, the luminescence band maxima of transdioxo complexes show a red shift and changes in the intensity distribution within the high-frequency vibronic progression involving the symmetric metal-oxo stretching mode, 9,10, 12 whose frequency shows a linear increase with pressure.…”